A few conclusions:
1) The plastic puck as it is now allows to see how the water level falls at the end of the extraction, but it ruins the puck in the first moments, so it's better to remove or improve it.
2) The "Fellini move" does not do any harm to the puck. It merely expands / rises and then compresses again. But the extra pressure makes it necessary to really tighten the portafilter in the group.
3) To show a 'perfect' extraction I will probably need to dose more and grind coarser. The top of the puck will maybe be so high you can't see over it with the camera close up, though.
4) There is no "puck jump" when pulling the lever / raising the piston, probably because this time I used a tamper that fit les tight, I tamped lightly and pulled the lever gently.
The puck goes through a number of phases:
1) dry grinds tamped: a semi-hard vulnerable pack
2) pre-infusion: getting soaked, preferably gently
3) wet puck no pressure: a flexible lush body, particles floating around above it
4) pressure changes: puck compacts and expands but keeps a very good seal around and below! Also during Fellini
5) water level falls, pressure falls, puck dries and air bubble escape sometimes suggesting the puck was damaged but it is not damaged during the active flexible-body phase